Need advice 🙏

Hello, I’m going to Thailand in early February with a return flight from Bangkok for the end of March, which is more than the 45 regulatory days. During this period, I only stay 3 weeks in Thailand and the rest in Laos and Cambodia. I applied for a tourist visa but they want accommodation reservations for half of the stay! How to get the visa and is it necessary since I don't stay 45 days in a row?

Thanks a lot for your advice 😊